The present invention relates to obturators for use on ammunition, and, more particularly, for obturators for use on 45 mm or higher caliber ammunition for smooth bore guns.
Obturators are used on projectiles for sealing combustion gases and guiding the projectile through a gun tube. In operation, an obturator seals gases between both the tube/obturator and obturator/projectile interfaces. It will be appreciated that obturator design is very critical in making a good seal in the gun tube in order to attain required muzzle velocity during firing. At the same time, the obturator should promote manual round chambering and extraction without the use of significant force. Obturators are usually discarded at muzzle exit and, since the weight of obturator is considered parasitic, it should be as light as possible without sacrificing functionality.
Traditional obturators are located in the forcing cone region of a gun tube and are usually slightly super-caliber. Initial pressurization moves the obturator forward so that it is compressed between the projectile and tube to create an initial seal. As generated pressure increases, the projectile moves with the obturator forward into the straight part of a tube. As the obturator contacts the gun tube bore surface, the obturator is subsequently pushed back due to its super-caliber size. As pressure continues to increase in the gun tube, the obturator again moves forward with the projectile. Before the present invention, the aforesaid complex movement of an obturator with the projectile required an additional sealing agent between the obturator and projectile. Typically the sealing agent used is a well-known room temperature vulcanizing sealant, called JRTV.
U.S. Pat. No. 6,453,821 to Fowler, et al. issued Sep. 24, 2002, entitled xe2x80x9cHigh-Temperature Obturator for a Gun-Launched Projectile,xe2x80x9d discloses an obturator for a projectile launched from a gun barrel. The obturator includes an annular ring that is fabricated from a high-temperature resistant composite material. The annular ring has an inner surface that is in contact with the projectile.
U.S. Pat. No. 6,419,235 to Han, issued Jul. 16, 2002, entitled xe2x80x9cSegmented Obturator Ring,xe2x80x9d discloses an obturator ring comprising two or more pieces each being a little larger than semicircle of the projectile obturator ring groove circumference. Each piece at natural position has equal or smaller radius than the radius of the obturator ring groove of a projectile; therefore, each piece expands to be in the projectile groove.
U.S. Pat. No. 6,295,934 to Tepera, et al. issued Oct. 2, 2001, entitled xe2x80x9cMid-body Obturator for a Gun-launched Projectile,xe2x80x9d discloses an obturator for a projectile having a mid-body annular groove that includes a shaped surface. The obturator includes an annular ring having an inner surface in contact with the shaped surface of the annular groove of the projectile. The annular ring further includes an outer surface. When the projectile is in the gun barrel, the outer surface of the annular ring contacts an inner surface of a bore of the gun barrel.
U.S. Pat. No. 6,223,643 to Muller issued May 1, 2001, entitled xe2x80x9cObturator for a Gun,xe2x80x9d discloses an obturation assembly for a gun of the type comprising a barrel of which a rear end defines a firing chamber having an obturation seat and the gun further having a breechblock, the obturation assembly comprising: an obturation set including an annular obturator pad for sealing against the obturation seat; an obturation spindle having a shaft and a head, the shaft extending coaxially through the obturator pad; a first shim for location between the obturation set and the breechblock, and a second shim for location between the obturation set and the head of the obturation spindle.
U.S. Pat. No. 6,085,660 to Campoli issued Jul. 11, 2000, entitled xe2x80x9cLow Spin Sabot,xe2x80x9d is directed to a discardable sabot including a first support and a second support, aft of the first support. At least one of the supports is a sealing support, configured to provide a substantially gas-tight seal with the barrel and effective to allow the sabot and the projectile to be propelled forward through the barrel by expansion of propellant gas behind the sealing support
U.S. Pat. No. 5,929,364 to Tortorici, et al. issued Jul. 27, 1999, entitled xe2x80x9cObturator Sealing Means for a Split Wedge/Breechblock Gun,xe2x80x9d is directed to an obturator for guarding the primary sealing surfaces of a step wedge breechblock gun from post-firing residue buildup. Their device includes an active tube insert for facilitating face seal force multiplication, out of bore lip and face seals, an in bore piston polymer with expanding residue guard, and an out of bore face seal with a residue-tolerant polymer.
U.S. Pat. No. 5,750,919 to Jehle issued May 12, 1998, entitled xe2x80x9cSelf-Adjusting Obturator for Projectile Launching,xe2x80x9d discloses an obturator wherein propellant pressure forces generated within the bore of a gun barrel are applied to a projectile through a self-adjusting obturator to prevent projectile blow by of propellant explosion products. The propellant forces are transmitted through a body of shock-absorbing fluid in the obturator.
U.S. Pat. No. 5,012,991 to Pinson issued May 7, 1991, entitled xe2x80x9cProjectile with an Obturator Incorporating a Motor,xe2x80x9d discloses a tube-launched projectile including an airframe with an open aft end, an optical fiber dispensing bobbin, and an obturator having a rocket motor attached to a hard point in the aft end of the airframe. The obturator forms a pressure vessel with insulated inner walls that contain rocket propellant and an igniter. An ejectable plug located in the rocket nozzle is expelled upon motor ignition.
U.S. Pat. No. 4,907,513 to Manion, et al. issued Mar. 13, 1990, entitled xe2x80x9cHigh Volume Obturator Assembly Method,xe2x80x9d discloses an obturating band of the despun variety manufactured within the channel of a projectile assembly. A split ring polymer pre-band is clamped around the band seat of the projectile assembly and the free ends are welded together to form a continuous ring around the diameter of the projectile assembly within the encircling channel.
United States Patent Office Publication H167 to Forster, et al. published Dec. 2, 1986, entitled xe2x80x9cProjectile Obturator,xe2x80x9d is directed to a multipurpose projectile obturator of composite, frangible construction where the obturator forms part of a projectile that is launched from an upstanding tube. The obturator is generally made up of an elastomeric band of a suitable grade of rubber.
U.S. Pat. No. 4,552,071 to Horais, et al. issued Nov. 12, 1985, entitled xe2x80x9cTwo-Piece Despin Obturator,xe2x80x9d is directed to a two-piece despin obturator mounted on a forwardly inclined obturator ramp on the projectile sidewall has a ring-shaped body of nylon-6 and a wiper band formed from Plascon nylon. The rotational velocity imparted to the ring is partially coupled as the inner surface of the ring rotates on the obturator mount of the projectile.
U.S. Pat. No. 4,444,113 to Campoli issued Apr. 24, 1984, entitled xe2x80x9cHigh-Pressure Self-Sealing Obturator in Sabot Discard Projectile,xe2x80x9d is directed to a high-pressure self-sealing obturator positioned to fit on the rear of a sabot assembly in a discarding projectile assembly to prevent the obturator from backing off during initial impact of bore walls by the projectile assembly. The obturator includes an extension and a groove for snapping a case mouth into the extension. The outer surface of the obturator conforms to the bore of the gun.
U.S. Pat. No. 4,242,961 to Moredock, et al. issued Jan. 6, 1981, entitled xe2x80x9cChevron Grooved Decoupling Obturator,xe2x80x9d is directed to an obturator for a projectile to be fired from a rifled barrel, with the obturator being mounted on the projectile in such a way as to permit rotational slippage. An external portion of the obturator ring has a plurality of encircling slots, essentially parallel to each other, which slots are rearwardly inclined so as to define a plurality of chevron-like members designed to forcibly engage the rifling of the barrel. The interior of the obturator ring is designed to slip rotationally with respect to the projectile body portion as the projectile travels along the barrel, thereby minimizing the rotation of the projectile as a result of rifling effects.
A family of wedge shaped obturators was previously developed in the United States for 120 mm tactical tank ammunition. Both a kinetic energy style obturator and a multipurpose style obturator were designed to generate contact pressures on the surfaces they are intended to seal that are almost equal to the gas pressures they are intended to seal out. Furthermore, both known obturators are initially inserted with clearance between the obturators and the smooth gun bore and must traverse a forcing cone to provide an initial low pressure seal that is needed to seat the obturators. If the seal between the obturator and gun tube is not established at low pressure, a seal cannot be established as the obturator travels down the gun tube.
Thus a significant drawback of known obturators is that they are not compliant enough to maintain a good seal with a changing gun tube profile. The U.S. Army""s Tank Extended Range Munition-Kinetic Energy (xe2x80x9cTERM-KExe2x80x9d), now called Medium Range Munition (xe2x80x9cMRMxe2x80x9d), projectile requires pre-translation of a round into the tube. Further, since obturators travel with the projectile, obturators will likewise be pre-translated into the tube. A puller sabot, for example, requires the obturator to be located forward of the forcing cone, this requires the obturator to be sub-caliber.
Referring now to FIG. 1, an example of an obturator for a projectile is shown in a partial cross-sectional view. There shown is an obturator 10 within a gun tube 12. The obturator 10 encircles a sabot 5 that, in turn holds a flight projectile 16. In accordance with prior art methods a JRTV or equivalent rubber-like material 14 fills gaps between the obturator and the sabot 5 and flight projectile 16. The JRTV material 14, while intended to maintain a seal, is difficult to work with in assembling the parts, and may pull away from abutting surfaces when the round is chambered. See, for example, FIG. 1 of U.S. Pat. No. 4,444,113, showing xe2x80x9crubber-like cover 38.xe2x80x9d
When a round is chambered in a gun tube pressure tends to move the obturator forward within the gun tube and radially outward to seal against the gun tube bore. However, as soon as the obturator contacts the gun tube bore, the resultant contact tends to push back on the obturator while the projectile is still moving forward. As the obturator moves back the JRTV under pressure pushes up against the projectile and the obturator loses contact with the JRTV opening a small crack between the obturator and the JRTV. As a result the desired seal is destroyed producing unwanted leaks that detrimentally effect performance upon firing the round.
The present invention avoids the drawbacks of the prior art, particularly with respect to eliminating dependence on JRTV for sealing.
The present invention provides an obturator for sealing between a projectile and a gun tube. The obturator includes at least one gun tube side cannelure. At least one projectile side cannelure is located opposite to the at least one gun tube side cannelure, where the at least one gun tube side cannelure is conformed to seal around the projectile. A tail protrudes from a rearward end of the at least one gun tube side cannelure, where the tail makes contact with the bore to make a low pressure seal. Initially, the tail may or may not interfere with the bore.
In contrast to the prior art, the invention provides obturators offering a lightweight mechanism to seal the gases in puller sabot, cased telescoped ammunitions (xe2x80x9cCTAxe2x80x9d) and/or ammunition used with a conventional tube having a forcing cone without dependence on JRTV sealing material for sealing between the obturator and the projectile.
In one aspect of the invention an obturator for puller sabots and CTA""s includes a flexible tail that provides an initial seal between tube and obturator. It also includes cannelures to provide significant seal all through the travel of a projectile through a gun tube.
In one aspect of the present invention an obturator generates contact pressure that is substantially greater than the gas pressure it is required to seal and the obturator includes flexible components that maintain the seal even when encountering sudden changes in bore diameter so that seal will be maintained under all conditions.
In another aspect an obturator constructed in accordance with the present invention includes a plurality of cannelures between the projectile and the obturator and also between the obturator and the gun tube, where the plurality of cannelures are combined with a moving wedge to generate very high contact pressures.
In another aspect an obturator constructed in accordance with the present invention is lightweight, compliant with changing gun tube profile, has no dependence on use of JRTV.